This invention relates to the production of an unique highly absorbent coating formulation, and its use to facilitate multi-color flexographic printing onto linerboard. Heavyweight linerboard is coated, printed upon, dipped into wax and converted into a carton for various packaging applications. A need has arisen for a highly absorbent coating for heavyweight linerboard which is compatible with high quality multi-color printing inks, thereby allowing the printing inks to dry quickly and maintain a high percentage of brightness even after waxing.
High water absorbency is required to aid in the ink drying process on a post print flexographic press. Post print flexographic presses do not ordinarily incorporate driers to cure the ink film during printing. Multi-color graphics require ink to dry rapidly, enabling additional layers of colored inks to be rapidly applied to the substrate maintaining print clarity and uniformity. The highly absorbent nature of the coating formulation solves the ink drying problem by rapidly absorbing the water from the colored ink. In addition, the unique formulation enables the multi-color high quality flexographic ink to maintain a high level of brightness after the converted carton has been coated with wax.
British patent No. 1,513,047 relates to a process for the production of coated lightweight paper with improved printing. The patent addresses lightweight papers which are used as printing supports for journals and cover pages of most magazines. The lightweight paper is said to have a weight range of 45 g/m.sup.2 to 100 g/m.sup.2. Disclosed is a thin coating for a lightweight paper wherein both sides of the paper is coated with a precipitated amorphous silicate. The two sided coating, embodying the disclosure, exhibits an increased elastic volume in the coating layers. The coated lightweight paper is then glazed on a calendar, eleven times, under a steady linear pressure. The resultant two-side coated lightweight glazed paper is now suitable for gravure or offset printing.
In contrast, the present invention provides an unique process for producing an unique formulation for enhancing multi-color flexographic printing for application to heavyweight linerboard. The linerboard, embodying the invention, has a basis weight greater than 150 g/m.sup.2. The linerboard is only coated on its gloss side to facilitate flexographic printing of multi-color inks and subsequent post print wax dipping. The thick coating formulation absorbs the water from the ink and allows for successive layers to be rapidly printed thereon.
In addition, British Patent No. 1,513,047 mentions that the synthetic amorphous silicate component embodying its coating is dispersed in the coating formulation with moderate stirring in the absence of high shear stressing. Applicant specifically incorporates the amorphous silicate into the coating formulation at high shear to facilitate formation of the formulation.
The linerboard coating embodying the present invention has an unique functionality for it intended product use.
In the post print process, successive layers of a pigment based aqueous ink are printed onto a containerboard. The containerboard is a conjugated multi-component structure made up of a fluted material known as a medium which is bonded on each side of the flute tips to linerboards. Without use of the unique coating formulation, embodied by the present invention, a specific drying step or method would be required after the deposition of each ink layer during flexographic printing. Such requirement would be economically prohibitive and slow the overall process. The process by which the ink is applied to the coated linerboard is flexography. In this printing process, an inductor roll is used to transfer ink from the ink pen to an anilox roll. The anilox roll is made up of a multitude of cells designed to contain a precise volume of ink. The ink is then transferred to a printing plate which deposits that volume of ink to the substrate. Multiple colors of ink would be applied to the coating. It is essential that the ink be dry prior to an additional application of ink. One function of the coating formulation is to absorb the inks liquid phase to effect drying. Silica and silicate products have been known to accomplish this via absorption.
Further, it is an objective of the present invention to produce a coating formulation that can maintain the brightness of an ink even after a wax coating has been applied to a converted carton.
It is a further object of the invention to improve print uniformity and quality of multi-color graphics in flexographic printing onto a heavyweight linerboard substrate.